A Usable, Secure Communications Protocol: Client-Side TLS - Implementing SSL/TLS Using Cryptography and PKI - page 360

Listing 6-66: “tls.c” with protection parameters sent to send_message
static int send_handshake_message( int connection,
int msg_type,
const unsigned char *message,
int message_len,
TLSParameters *parameters )
{
…
return send_message( connection, content_handshake, send_buffer,
send_buffer_size, &parameters->active_send_parameters );
…
static int send_alert_message( int connection,
int alert_code,
ProtectionParameters *parameters )
{
…
return send_message( connection, content_alert, buffer, 2 , parameters );
…
static int send_change_cipher_spec( int connection, TLSParameters *parameters )
{
…
send_message( connection, content_change_cipher_spec, send_buffer, 1,
&parameters->active_send_parameters );
…
static int receive_tls_msg( int connection,
TLSParameters *parameters )
{
…
if ( ( status = send_alert_message( connection, illegal_parameter,
&parameters->active_send_parameters ) ) )
…
read_pos = parse_server_hello( read_pos, handshake.length, parameters
);
if ( read_pos == NULL ) /* error occurred */
{
send_alert_message( connection, illegal_parameter,
&parameters->active_send_parameters );
…
read_pos = parse_finished( read_pos, handshake.length, parameters );
if ( read_pos == NULL )
{
send_alert_message( connection, illegal_parameter,
&parameters->active_send_parameters );
Notice that the alert messages need to be updated, too. If an alert is sent after
a handshake has completed, the alert itself must be encrypted. Although this
won't come up during an initial handshake, send_alert_message must include
a ProtectionParameters value because send_message does.